Superconductivity of Pure H₃S Synthesized from Elemental Sulfur and Hydrogen

Abstract

Superconductive H3S synthesized from H2S is very poorly crystallized, and has\nexcess sulfur as impurity (3H2S -> 2H3S + S). The phase transition process\nundergoes in sulfur excess condition, which might cause hydrogen deficiency.\nThe influence of hydrogen deficiency is not clear. Therefore investigation on\nthe superconductivity in H3S with no hydrogen deficiency is demanded. Two\ngroups performed synthesis of H3S from elemental sulfur and hydrogen (direct\nsynthesis) and their results have shown that no hydrogen deficiency is caused\nwhen the direct synthesis is performed under hydrogen excessive condition.\nHowever, no measurements of superconductivity has been carried out because of\nthe major technical difficulties in hydrogen experiments in diamond anvil cells\n(DACs). Here, we report the first electrical resistance measurements in\nsuperconductive H3S synthesized from elemental sulfur and hydrogen (3H2 + 2S ->\n2H3S). Our powder X-ray diffraction (PXRD) using a synchrotron X-ray revealed\nthat synthesized H3S has much improved crystalline quality and no sulfur as\nreported in previous works. We observed a superconducting transition with a\nsharp drop of the resistance at Tonset = 200 K and we obtained the highest\nToffset of 186 K in S-H system.\n